In a mass spectrometer, a method in which ions generated at an atmospheric pressure or in a low vacuum are introduced into a mass analyzing part requiring a high vacuum of 10−1 Pa or lower is an important technique for realizing a high sensitivity.
Analytical Chemistry, 2007, 79, 20, 7734-7739, Adam Keil, et al. discloses a method in which a thin capillary is coupled directly between an atmospheric ion source and a mass analyzing part of a high vacuum. In this method ions are introduced into the mass analyzer through the thin capillary.
U.S. Pat. No. 6,177,668 discloses a differential pumping system that is most generally used in mass spectrometry. In this system, a single or multiple differential pumping chambers each having an intermediate pressure is installed between the atmospheric ion source and a vacuum chamber, and gas is evacuated from those differential pumping chambers by a pump to enable ions generated at the atmospheric pressure to be introduced remarkably efficiently as compared with Analytical Chemistry, 2007, 79, 20, 7734-7739, Adam Keil, et al.
WO 2009/023361 discloses a method in which a pulse valve is installed between the atmospheric ion source and a high vacuum unit in which the mass analyzing part is equipped, and open/close operation of the pulse valve is temporally controlled. When the pulse valve is opened, ions are introduced into the mass analyzing part of the high vacuum unit, and then after the pulse valve is closed to reduce a pressure in the high vacuum unit, the mass analyzing part is operated. As a result, the amount of introduced ions can be increased infinitely more than that of Analytical Chemistry, 2007, 79, 20, 7734-7739, Adam Keil, et al.
Japanese Unexamined Patent Application Publication No. 2001-147216 discloses a method in which a material having substantially the same ionization efficiency as that of a sample, for example, a stable, rare and isotopically substituted material of the sample is added with a constant concentration as the internal standard to measure the amount of ions.